Power transmission



R. S. MILLER POWER TRANSMISSION July 22, 1941.

Filed Feb. 19', 1940 2 Sheets-Sheet 1 w i z i .6 2 8 6 2 5O 0 w I 7 M. E a m 7% a m. y w m \m M 1 w 0 6 m 8 8 F Z T o 9 9 a 4 l o I & m J, U. z a M 2 if f w 1 M #ORNEY ly 22,19 1. R. s. MILLE'R 2,250,389

POWER TRANSMISS ION Filed Feb. 19, 1940 2 Sheets-Sheet 2 v INVENTOR RAYMOND MILLER ATTORNEY Patented July 22, 1941 POWER TRANSMISSION Raymond S. Miller, Detroit, Mich., assignor to Vickers Incorporated, Detroit, Mich., a corporation of Michigan Application February 19, 1940, Serial No. 319,600 6 Claims. (Cl. 60- 52) This invention relates to power transmissions,

- particularly to those of the type comprising two or more fluid pressure energy translating devices one of which may function as a pump and another as a fluid motor.

The invention is particularly concerned with a power transmission system for operating a press or the like and which is adapted to provide a special operating cycle in which the press ram or other motor moves in an advancing direction until a predetermined high pressure is reached at which time a predetermined lower pressure will be maintained on the work for a predetermined interval before returning the press ram or other hydraulic motor.

A further object is to provide an improved pressure limiting valve for use in a hydraulic power transmission system of the character described.

,Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred form of the present invention is clearly shown.

In the drawings:

Figure 1 is a diagrammatic view of a power transmission system incorporating a preferred form of the present invention.

Figure 2 is a longitudinal cross section of a special pressure limiting valve forming part of the circuit in Figure 1. e

Figure 3 is a longitudinal section taken on line 3-3 of Figure 2.

Figure 4 is a transverse section taken on line 4-4 of Figure 3.

Figure 5 is a fragmentary sectional view taken on the line 5-5 of Figure 4.

Referring now to Figure 1, there is illustrated a conventional source of pressure fluid comprising a fixed displacement pump Ill adapted to be driven by an electric motor I2. The pump I0 has a suction conduit I4 through which oil is withdrawn from a tank I6 and pumped into a delivery conduit I8, The latterhas a relief valve 20 of any suitable construction adapted .to bypass oil to the tank through a conduit 22 whenever a predetermined pressure is exceeded in the delivery conduit I8. The conduit I8 leads to the pressure port 24 of a pilot-operated four-way valve 26. The latter has tank ports 28 and 38 which connect to the tank I6 by a conduit'32. The motor port 34 of valve 26 connects by a conduit 36 with a port 38 of a combined pressure limiting and pilot control valve 40. From a second port 42 of thevalve a conduit 44 extends to a port 46 of a pressureoperated sequence valve 48. A second port 50 of the valve 48 connects by a conduit 52 with the booster cylinders 54 of a hydraulic press. From the other cylinder port 66 of valve 26 a conduit 58 extends to the pull-back cylinders 60 of thepress. The valve 48 has a third port 62 which connects by a conduit 64 with the tank I6. The valve 48 has a third port 66 which connects by a conduit 68 with a port I8 of a pressure-operated sequence valve I2 which may be similar to the valve 48. A second port I4 of valve 12 communicates by a conduit I6 with the closing cylinder I8 of a prefill check valve which may be of conventional construction. An opening cylinder 82 of the latter connects by a conduit 84 with the conduit-58 and the pull-back cylinders 60. The prefill check valve 80 controls communication between the tank I6 and a conduit 86 leading to the main cylinder 88 of the hydraulic press. The latter has a ram 90 which carries the press platen 92 reciprocable in the usual slide ways, not shown. The platen also connects by rods 94 with pistons 96 which separate the booster cylinders 54 from the pull-back cylinders 68. The sequence valve I2 has a third port 98 which connects by a conduit I00 with the conduit 86 leading to the main cylinder 88.

The righthand pilot operating chamber I02 of the valve 26 communicates by a conduit I04 with a port I06 in the upper part of the valv 40. An adjacent port I88 communicates by a conduit IIIl with a branch conduit II2 leading from the delivery line I8. The branch conduit II2 extends to the pressure port P of a rotary three- -way pilot valve H4. The tank port T of valve I I4 connects by a conduit I I6 with the tank conduit 64, branches H8 and I20 serving to drain seepage from the end chambers of sequence valves 48 and I2. Port 2 of valve H4 is plugged while port I connects by a conduit I22 with a port lefthand operating chamber I24 of valve 26, A

I26 at the upper part of valve 40 is connected by a branch conduit I28 with the pullback cylinder conduit 58. Each of the valves thus far described with the exception of valve 40 is of well-known construction so that a brief description of each will sufiice to to those skilled in the art.

Valve 26 is of the type which, when once shifted by pilot pressure to either'its righthand or 'leithand position, remains in that position I Suitable until shifted again by pilot pressure. detent means, not shown, may be provided for this purpose. When pilot pressure is admitted to identify them the lefthand operating chamber I24, the spool shifts to the right connecting pressure port 24 to motor port 34 and connecting motor port 56 to tank port 28. When pilot pressure is admitted to the righthand operating chamber I02, the

, spool shifts to the left transposing the pressure port 66 and 98 respectively. The setting of these valves is such that a slightly higher pressure is required to open valve I2 than to open valve 46. The prefill valve 80 acts as a check valve to admit oil freely from the tank to the main cyclinder when no pressure exists in either chamber I8 or 82. When closed by pressure in chamber I8, no flow in either direction can take place, and when opened by pressure in chamber 82, reverse flow can take place from the main cylinder to the tank.

Before describing the detailed construction of the valve 40, its general function will be described together with the operation of the entire system shown in Figure 1. One function of valve 40 is to act as a relief valve to limit the pressure in conduits 36 and 44 (which are always in communication) by dumping excess oil to tank through port 62 and conduit 64. In so doing the valve 40 operates firs-t as a high pressure limiting valve and then, when this pressure has been reached, immediately changes so as to act as a lower pressure limiting valve. In other words, the valve 40 does not open to port 62 until a predetermined high pressure has been reached, but as soon as this pressure has been reached the valve thereafter maintains a predetermined lower pressure on the oil in ports 38 and 42. The valve 40 also acts as a pilot controlling valve for determining the supply of pressure or exhaust to and from the pilot operating chamber I02 of valve 26. Its action in 'this respect is likewise controlled in response to the building up of the predetermined high pressure with the additional function of providing a time delayed action. In other words, a predetermined interval after the high pressure has been reached valve 40 admits pilot pressure from port I08 to port I06. Port I06 is cut oil from the pilot pressure and connected to exhaust whenever pressure is admitted to the port I26.

In operation, with the motor I2 driving the pump I0 and with the valve 26 in the lefthand position illustrated, oil is withdrawn from the tank I6 through suction conduit I4 and delivered' through conduit I8, through ports 24 and 56 of valve 26, and conduit 58 to the pull-back cylinders 60. Since the platen 82 is in its upper position the oil cannot flow into pull-back cylinders 60 so that the entire pump delivery must escape through the relief valve 28. Ordinarily this valve isset to open at a pressure slightly higher than that at which valve 48 opens,

To start a pressing cycle, the-handle I88 1:

moved clockwise admitting pilot pressure to port I-, conduit I-22 and operating chamber I24. The

valve 26 accordingly shifts to the right admitting pressureoil to pipe 36 where it flows through valve 40, conduit 44, valve 48 and conduit 52 to the booster cylinders 54. The platen accordingly descends, preflll valve opening as a check valve to permit free flow from the tank I6 through conduit 86 to the main cylinder 88. Oil discharged from the pull-back cylinders 60 returns to tank through conduit 58, ports 56 and 28 and conduit 32.

As the platen meets the work, pressure builds up in the booster cylinders 54 and is transmitted back through conduit 52 to valve 48 causing the latter to open admitting pressure oil also through port'66, pipe 68, valve I2 and conduit 16 to the closing chamber I8 of the prefill check valve 80. As soon as the latter closes, pressure continues to build up, opening valve I2 and admitting pressure oil to conduit I00 and 86 where it is effective in the main cylinder 88. The press continues to advance at a slower rate, and as the resistance imposed by the work increases, the pressure in the pump delivery line increases. When this reaches a predetermined value, valve 40 will open bypassing the pump delivery to tank through conduit 64 at this point.

Immediately thereafter the internal mechanism of thevalve shifts so as to effect this bypassing at a lower pressure. There is also set in motion a time delay mechanism which is effective a predetermined time after the peak pressure occurs 'to connect ports I06 and I08 thereby admitting pilot pressure through conduits H0 and I04 to the pilot operating chamber I02. The valve 26 is accordingly shifted to the left thus connecting the pump delivery to port 56 where it is delivered through conduit 58 to the pull-back chambers 60. The platen accordingly ascends discharging oil from the booster. cylinders 54 through conduits 52, 44 and 36, ports 34 and 30, and conduit 32 to tank. Pressure oil in conduit 58 is also transmitted through branch conduit 84 to the opening chamber 82 of preflll valve 80 thus opening a free path for return of oil from the cylinder 88 to tank.

Referring now to Figures 2 through 5, the internal construction of the valve 40 is there illustrated. As will be seen from Figure 2, the lower part I3I of the body is formed in the shape ofa pipe T in which the three ports 38. 42 and 62 are located. A conical valve I32 cooperates with a seat I34 to normally close off, a chamber I86, which connects ports 38 and 42. from communication with the port 62. Valve I82 is biased to closed position by a spring I38 and has a piston I 40 slidable in a chamber I42 whereby the valve may be operated by fluid pressure. A restricted passage I44 connects the chamber I42 with the chamber I36 so that at all times when there is no flow out of the chamber I42 the pressure therein will be the same as the pressure in chamber I36. The chamber I42 communicates through passages I46 and I48 (Figure 3) with a pilot relief valve I50 which in the form shown consists of a spring-loaded ball valve, the spring I52 of which is adjustable by means of an abutment screw I54. The setting of the spring I52 determines the value of the high pressure at which the valve I32 opens. In its operation it is similar to that of the relief valve disclosed in the patent to Harry F. Vickers, 2,043,453. j

The exhaust side of the valve I58, however, is not connected to tank as is the case with the valve in the aforementioned patent but communicates through passages I56 and I58 with a chamber I60 formed in the righthand end of a cap member I62 which forms the upper part of the main body of the valve 40. This chamber I60 is closed by an end cap I63. Slidably mounted in a bore I64, and projecting into the chamber I60 is a valve spool I66 normally biased to the left by a spring I68. The latter abuts against a shoulder I10 formed on a second slidable spool I12 which is also mounted in the bore I64 and projects into a chamber I14 in the righthand end of the cap member I62. The construction is such that the two spools I66 and I12 are freely slidable as a unit in the bore I64 without compressing spring I68. If one spool meets resistance to movement, the other spool may be moved toward the one spool by compression of the spring I68.

An end cap I16 closes the chamber I14 and contains an adjustable 'needle valve I18 which controls the rate at which fluid may be exhausted from chamber I14 throu'gh passages I80 and 3 M2, the latter leading to the port I26. When pressure oil is admitted to port I 26 the latter may flow freely to the chamber I14 through passage I82, a check valve I84 and a passage I86. Thus when the port I26 is connected to tank, that is, during the downward stroke of the press when conduits 58 and I28 are connected to the tank conduit 32, pressure exhausting from the pilot relief valve I50 and entering the chamber I60 will push the valve spool I66 to the right in Figure 2 and will also tend to push the valve spool I12 to the right. valve spool I12 can move, however, is determined by the setting of the needle valve I18 which permits oil to exhaust from chamber I14 only at a reduced rate. Thus the spool I66 can move immediately through its full stroke compressing spring I68 which urges the spool I12 to the right as fast as the rate of exhaust from chamber I14 will permit.

The valve spool I66 in its normal position, shown, blocks communication between a passage I68 leading to chamber I42 and a passage I90 communicating with the passage I58. When the spool I66 shifts to the right, connection is established between these passages. This permits the pressure in chamber I 42 to be transmitted directly to the chamber I60 regardless of the opening of valve I50. It also connects the chamber I42 to a low pressure pilot relief valve I92 (Figure 3). For this purpose the passage I56 is extended to the left beyond the passage I56 in Figures 3 and 4 and connects by passages I94 and I96 with the relief valve I92. The latter is also formed as a spring-loaded ball valve, the spring I98 of which is adjustable by an abutment screw 200 and is adjusted to open at a lower pressure than the valve I50. The exhaust from valve I92 passes through a passage 202 (Figure 5) which intersects the bore I64 at its center point. The center of the bore is also in communication with tank through a passage 204 (Figure 2) which communicates with a cylindrical chamber 206 in which a pilot extension 208 of the valve I32 is slidable. The diameter of the extension 208 is preferably the same as the efi'ective diameter of the seat I34. The valve I32 is provided with a central bore 209 having a small extension 2I0 which leads to the chamber at the lower side of the seat I34 which is always in communication with tank through conduit 64.

The valve spool I12 in its normal position,

The rate at which the illustrated, connects the port I06 through a passage 2 I2 in the body I62 and through an annular groove 2I4, radial holes 2I6 and central bore 2I8 in the spool I12, with the central portion of bore I64 which is in communication with the tank as was just described. When the spool I12 is shifted to the right, an annular groove 220 connects passage 2 I2 to a passage 222 leading to port I08 and cuts ofi communication between passage 2I2 and tank.

It will thus be seen that as a prerequisite to any change in position of any of the parts in valve 40 from the position illustrated in Figures 2 through 4, the pressure in chamber I36 must rise to a value sufficient to open valve I50. -When this pressure is reached the latter valve will open exhausting oil from the chamber I42 at a rate faster than it can be admitted through restricted passage I44 thus setting up a pressure difference between chambers I42 and I 36 causing the piston I40 to lift against the bias of spring I38. The oil exhausted from valve I50 flows through passages I56 and I58 to the chamber I60, immediately shifting the spool I66 which compresses spring I68 and biases the spool I12 to the right. This shifting of spool I66 connects chamber I42 through passages I88, I and I58 to the chamber I60 thus maintaining pressure thereon, and also connects chamber I42 through passages I56, I94 andI96 to the low pressure relief valve I92. Thus the oil in chamber I42 is permitted to exhaust more easily through the valve I92, passage 202, bore I64, passages 204, 206 and 2H) to tank. Piston I40 accordingly lifts higher until the valve I32 reaches a position where the full pump delivery may be exhausted therethrough at a pressure equal to the setting of valve I92 plus the bias of spring I38 applied to the area of the piston I40. I

The compression of spring I68, at the same time, starts the spool I12 moving to the right at a speed determined by the setting of needle valve I18. When this rightward travel of spool I12 is completed, port I06 is cut oil from tank communication and connected to port I08 through passages 2I2,' 220 and 222. Thus pilot pressure may be admitted from port I08 to port I06 shifting the valve 26. When the valve 26 is shifted, port I26 now becomes connected to the main pump delivery line thereby admitting pressure oilthrough passage I82, check valve I84 and passage I86 to the chamber I14. The spool I12 is accordingly shifted to the left. Spool I66 is now free to move to the left by discharging oil through passages I56 and I56 and through a branch passage 224 (Figure 3) and a check valve 226 which leads to the passage I46 and chamber I42. Since the chamber I36 is now at tank pressure, thisoil may exhaust from chamber I42 through the restricted passage I44 thus permitting spool I66 to 'return to the position illustrated. -The connecmight be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. In a hydraulic power transmission system for operating a press or the like the combination of a hydraulic motor, pump means for supplying fluid under pressure to operate the motor, directional control means for directing the pump delivery to operate the motor in an advancing or in a returning direction, means for limiting the pressure in the motor advancing conduit to a predetermined high value, a second means, normally ineffective, for limiting the pressure in the motor advancing conduit to a predetermined low value, means operated when the pressure in the motor advancing conduit reaches said high value for rendering the second pressure limiting means effective, and time delay means started concurrently with operation of the last-named means for shifting the directional control means to return the motor.

2. In a hydraulic power transmission system for operating a press or the like the combination of a hydraulic motor, pump means for sup plying fluid under pressure to operate the motor, directional control means for directing the pump delivery to operate the motor in an advancing or in a returning direction, means, normally ineffective, for limiting the pressure in the motor advancing conduit to a predetermined low value, means operated when the pressure in the motor advancing conduit reaches a predetermined high value for rendering the pressure limiting means effective, and time delay means started 00110111- rently with operation of the last-named means for shifting the directional control means toreturn the motor.

3. In a hydraulic power transmission system for operating a press or the like the combination of a hydraulic motor, pump means for supplying fluid under pressure to operate the motor, directional control means for directing the pump delivery to operate the motor in an advancing or in a returning direction, means, normally ineifective, for limiting the pressure in the motor I advancing conduit to a predetermined low value,

means operated when the pressure in the motor advancing conduit reaches a predetermined high value for rendering the pressure limiting means eiiective, and'means for limiting the effective op-' for operating a press or the like the combination of a hydraulic motor, pump means-for supplying fluid under pressure to operate the motor, directional control means for directing the pump delivery to operate the motor in an advancing or in a returning direction, means for limiting the pressure in the motor advancing conduit to a predetermined high value, a second means, normally ineffective, for limiting the pressure in the motor advancing conduit to a predetermined low value, each of said pressure limiting means including a pilot relief valve, both of said relief valves being arranged to control a single main relief valve in said motor advancing conduit, and means operated when the pressure in the motor advancing conduit reaches said high value for rendering the second pressure limiting means effective.

5. In a hydraulic power transmission system for operating a press or thellike the combina-- .tion of a hydraulic motor, pump means for supplying fluid under pressure to operate the motor, directional control means for directing the pump delivery to operate the motor in an advancing or in a returning direction, means for limiting the pressure in the motor advancing conduit to a predetermined high value, a second means, normally ineffective, for limiting the pressure in the motor advancing conduit to a predetermined low value, each of said pressure limiting means including a pilot relief valve, both of said relief valves being arranged to control a single main relief valve in said motor advancing conduit, and means operated when the pressure in the motor advancing conduit reaches said high value for rendering the second pressure limiting means effective, said last means including a third pilot valve for controlling communicaton between the second pilot relief valve and the main relief valve.

6. A'two-pressure relief valve and pilot controlling valve comprising in combination a pilotcontro'lled main relief valve, a first pilot relief 'valve and a second pilot relief valve arranged to a open the main relief valve at a predetermined low pressure, means normally rendering the second pilot relief valve ineffective and responsive to opening of the first pilot valve for rendering the second pilot valve eflective, a pilot valve, and means responsive to opening of the first relief valve for shifting the pilot valve after a predetermined time interval.

RAYMOND S. MILLER. 

